Microcrack propagation in Cu metal films on a flexible PI substrate during cyclic-bend testing

Cyclic-bend testing of flexible copper clad laminate (FCCL) was conducted to investigate microcrack propagation in electroplated Cu metal films on a flexible polyimide (PI) substrate. During the cyclic-bend testing process, a zigzag pattern of microcracks was developed perpendicular to the loading direction. Electron backscattered diffraction (EBSD) analysis was conducted on the surface planes of un-deformed (i.e. as-received) and deformed Cu metal films to obtain the crystallographic orientation mappings. EBSD analysis revealed that an intergranular type of microcrack propagation was predominant during the cyclic-bend testing. Most of the microcracks were propagated along the high angle grain boundaries (HAGBs) instead of the Σ3 twin boundaries (TBs). EBSD analysis also revealed that microcracks tended to propagate into the HAGBs separating neighboring grains with a high Schmid factor (SF).